Laboratory of Rare Earth Intermetallics
Chair of General Physics and Magneto-Ordered Matter
Faculty of Physics
M.V. Lomonosov Moscow State University
Vorobjovy Gory, 119992 Moscow,
Russia
Head of the Laboratory - Leading researcher, Professor Ashot Markosyan
Members of
the Laboratory
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1 |
Leading researcher, doctor of physical and
mathematical science (habilitation degree), Professor for majors |
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2 |
Associate Professor, candidate of physical
and mathematical science (Ph.D. degree) |
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3 |
Senior researcher, candidate of physical and
mathematical science (Ph.D. degree) |
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4 |
Research associate, candidate of physical and
mathematical science (Ph.D. degree) |
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5 |
Physicist, candidate of physical and mathematical science (Ph.D. degree) |
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6 |
Vladimir
Uryvaev |
Undergraduate student, 5th year |
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From left to right: Granovsky S.A., Rodimin V.E., б Gaidukova I.Yu, Dubenko I.S., Markosyan A.S.
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General information on the
scientific activity
The scientific interests of the group include
various magnetic phenomena in materials containing 4f and 3d elements. The
primary research work is related to the study of magnetic phase transitions in
rare earth (RE/R) intermetallic compounds with transition elements of the iron
group, i.e. R-3d intermetallics. Among the large variety of R-3d intermetallics
one can find materials important for technical applications and modern
technology, such as permanent magnets, magnetostrictive devices, elements for memory
recording systems, and model compounds of current interest for basic research
[1].
In the contemporary physics of magnetic
phenomena, magnetism of the R-3d intermetallics is one of the most popular and
most developing directions that draws attention of many explorers. Two magnetic
subsystems of different nature are incorporated and contribute to magnetism in
these compounds. One of them, the 4f-subsystem, is made up of the localized
4f-electrons and can be described well by atomic characteristics of the RE ions. The latter
one, the d-subsystem, is formed as a result of the hybridization of the
itinerant 3d-electrons of the transition metal and 5d-electrons of RE.
Magnetism of this itinerant subsystem is usually described by characteristics of the hybridized
3d-5d band (d-band). Thus, the R-3d intermetallics combine the
properties specific for both, 4f-metals (large anisotropic magnetostriction, Dl/l
> 10-3, and large energy of the magneto-crystalline anisotropy, Ha > 10 T) and 3d-metals
(magnetovolume effect DV/V of
the order of 10-3, high values of TC
exceeding substantially the room temperature).
The laboratory has different equipment for
synthesis of alloys and intermetallic compounds and their heat treatment under
controlled atmosphere: arc and induction furnaces, several resistance furnaces.
We have in our disposition an X-ray diffractometer and an optical microscope
for metallographic analysis. The low-temperature and high-temperature cameras
that can be mounted on the diffractometer allow to study the thermal expansion
of solids in a wide temperature interval from 5 to 900 K. Using this facility,
magnetic and structural phase transitions, magnetoelastic distortions of the
crystal structure (anisotropic magnetostriction), Invar (magnetovolume) effect
can be studied.
The members of the group carry out studies of
the magnetic and transport properties of the R-3d intermetallic compounds, in
which the magnetic state of the itinerant-electron subsystem can change
abruptly, by a first-order type phase transition, when varying external forces
(e.g., pressure, temperature or a magnetic field). It is usually said of a
magnetic instability of the itinerant magnetic subsystem in such compounds. Itinerant-electron metamagnetism, a
field-induced ferromagnetism in an itinerant-electron paramagnet by a
first-order type phase transition, is a particular case of the magnetic
instability.
While the number of binary R-3d intermetallics
is over several hundred, there are thousands among the ternary R-3d-M systems. In
the area of the ternary intermetallics with the chemical formula RmTnMp,
the compounds in which the R and 3d sublattices order independently at
different temperatures interest our research group. In particular, we study the
magnetic properties of the RMn2Ge2 and RMn2Si2
series.
Among the scientific
achievements of the team are:
- In RMn2 intermetallic compounds, the
magnetic ordering of the Mn subsystem has been found to occur through a
first-order type phase transition. It is accompanied by a giant volume effect DV/V ~
10-2 [2, 3] (Fig. 1).
- First experimental observation of the
phenomenon of field-induced itinerant-electron metamagnetism in the
pseudobinary compounds Y(Co1‑xAlx)2 [4] (Fig. 2).
- Discovery of the phenomenon of
temperature-induced itinerant-electron metamagnetism in RCo3
compounds with magnetic RE [5] (Fig. 3).
These works stimulated studies of different
aspects of a magnetic instability of the itinerant-electron subsystem in RMn2,
RCo2, and RCo3 compounds in many research institutions and universities.
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Fig. 1. Temperature dependence of the lattice
parameters of YMn2 in the paramagnetic (cubic crystal structure of
the MgCu2‑type) and antiferromagnetic (tetragonal) phases
[2]. Below TN ~ 90 K
the paramagnetic and antiferromagnetic phases co-exist. The volume effect at TN reaches ~ 6 % (the highest
value of the effect known for magnetic materials). (c-a)/a
= -2.6ґ10-3 at 5 K. |
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Fig. 2. Magnetization curves of the Y(Co1‑xAlx)2 compounds at 4.2 K [4]. The compounds
with x < 0.1 are itinerant-electron
paramagnets, and the external magnetic field induces a metamagnetic
transition from a paramagnetic to a ferromagnetic state. In the compounds
with x > 0.1, the
metamagnetic transition occurs from a weak-ferromagnetic to a strong-ferromagnetic
state. This effect is a consequence of a field-induced increase of the
density of d-electron states at the Fermi level. |
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Fig. 3. Temperature dependence of the
relative volume change of ErCo3 and HoCo3 normalized to
the room temperature [6]. Below TC,
a positive magnetic contribution in the thermal expansion appears smoothly
due to a magnetic ordering of the itinerant d-electron subsystem
(weak-magnetic state). The extra volume expansion at low temperatures (65 K
for ErCo3 and 180 K for HoCo3) is a consequence of
temperature-induced itinerant-electron metamagnetism of the d-subsystem when
the intersublattice molecular magnetic field HRCo
reaches the critical value by decreasing temperature. |
Scientific collaboration with
Russian Institutions
1.
Faculty
of Physics, Ural State University (Ekaterinburg)
2.
Saint-Petersburg
Institute of Nuclear Physics (Gatchina)
3.
Moscow
Institute of Radio- Engineering Electronics and Automation (MIREA)
International scientific
relations and collaboration
1.
Laboratoire
du Magnetisme L. Nйel (Grenoble,
France)
2.
Laboratoire
Leon Brillouin (Saclay,
France)
3.
Van der Waals - Zeeman Institute, University of Amsterdam (Netherlands)
4.
Institute
of Solid State Physics, Vienna University of Technology (Austria)
5.
Institute
of General Physics, Dresden Technical University (Germany)
6.
Institute
of Physics of the Czech Academy of Science, Prague (Czech Republic)
7.
Institute
of Solid State Physics, Tokyo University (Japan)
8.
Institute
for Molecular Science, Okazaki National Research Institutes (Japan)
9.
Physics
Department, Southern Illinois University, Carbondale (USA)
10. Centro Brasiliero de Pesquisas Fisicas, Rio de Janeiro
(Brasil)
11. Institute for Metal Research, Shenyang (People
Republic of China)
References
1. A.S. Markosyan, Magnetism of alloys of 4f (R) and 3d
elements (T), Encyclopedia of Materials:
Science and Technology, Elsevier Science Ltd. (2001) Vol. Magnetism,
pp. 78-85.
2. I.Yu. Gaidukova, A.S. Markosyan, A first-order structural
phase transition in the paramagnetic compound YMn2, Fiz. Met. Metalloved. 54 (1982) 184-186 (in Russian) [Phys. Met. Metallogr. 54 (1982) 168-170].
3. I.Yu.
Gaidukova, S.B. Kruglyashov, A.S. Markosyan, R.Z. Levitin, Yu.G. Pastushenkov,
V.V. Snegirev, Metamagnetism of the manganese subsystem in the RMn2
intermetallic compounds, Zh. Eksp. Teor.
Fiz. 84 (1983)
1858-1867 (in Russian) [Sov. Phys. JETP
57 (1983) 1083-1088].
4. V.V. Aleksandryan, A.S. Lagutin, R.Z. Levitin, A.S.
Markosyan, V.V. Snegirev, Metamagnetism of the itinerant d-electrons in YCo2:
investigation of the metamagnetic transitions in Y(Co1‑xAlx)2, Zh.
Eksp. Teor. Fiz. 89
(1985) 271-276 (in Russian) [Sov. Phys. JETP
62 (1985) 153-155].
5. N.
Ali, I.S. Dubenko, I.Yu. Gaidukova, A.S. Markosyan, V.E. Rodimin, Temperature
induced magnetic instability in the itinerant Co subsystem of the Er1‑xYxCo3 compounds, Physica B
281&282 (2000) 696-698.
6. E.
Gratz, A.S. Markosyan, I.Yu. Gaidukova, V.E. Rodimin, St. Berger, E. Bauer, H. Michor,
Temperature induced itinerant electron metamagnetism in ErCo3 and
HoCo3: influence of an external field and pressure, Solid State Commun. 120 (2001) 191-194.